According to a skipper Rossage (a self confessed ladies man with a penchant for young ladies and quiche) on a recent Hen Party on a yacht in the Isle of Wight a "Gentleman's Cocoa" is slang for a male masturbation.

Skipper Rossage told us that men on average have FOUR "Gentleman's Cocoa"'s a day!
or that Skipper is a "Gentleman's Cocoa"